Brigham Young taught that the Unity of the Church comes from revelation through the Holy Ghost.
"When the Chinese receives the Gospel he is one with us. He does not want six months' teaching or trial; he does not need to go to an academy or a seminary five or seven years to learn that this mode of baptism is correct; but taking the Bible he reads it, and, says he, "The Holy Ghost bears witness to me that baptism by immersion is the correct mode, and that it is right to break bread and drink wine in remembrance of, and to testify our faith in him whose body was broken and whose blood was shed for the salvation of the human family." There is no contention, and though only one Elder may have gone there, and he has baptized but one, or ten, a hundred, a thousand, or thousands, they are all of one heart and one mind; and if we were to charge this Elder not to tell these Chinese that they must gather to America, for that was the land of Zion—and America is the land of Zion—the first this Elder would know, somebody or other would be up in a meeting and telling that Zion was in America, and they had got to emigrate there. The Elder might inquire why, and he would be told, "It is revealed to me, and I do know by the manifestations of the Spirit within me, through your preaching, that we are to assemble on the continent of America, for that is the land of Zion." And if they come here, they will not ask how many methods of baptism we have, or how many of administering the Sacrament, or of dispensing the ordinances of the house of God, for the Spirit makes them of one heart and one mind with those on this continent, and from whatever nation they come, they all see alike in reference to the ordinances of the house of God." (Brigham Young, Journal of Discourses, vol 15, discourse 18, page 121-129)
Insofar as we have the Holy Ghost, we will be one. When we see members within the church fighting against the truth you can put it down in writing that such a member has not the Holy Ghost. When we see members fighting the brethren, we should know they have lost the spirit.
2 Nephi 18:20 To the law and to the testimony; and if they speak not according to this word, it is because there is no light in them.